Method of cleaning an evaporator

Abstract

A method of cleaning an evaporator that includes at least one heat transfer element for the evaporation of water, comprising forming a sacrificial layer of a first material on a surface of the heat transfer element (1); evaporating water that includes a second material to deposit the second material on top of the sacrificial layer (2, 3); and cleaning the evaporator by removing both the sacrificial layer formed on the heat transfer element and the second layer formed on top of the sacrificial layer; wherein the first material is more easily removed from the heat transfer element than the second material (4).

The invention claimed is: 
     
       1. A method of cleaning an evaporator that includes at least one heat transfer element for evaporation of water, the method comprising: forming a sacrificial layer of a first material on a surface of the at least one heat transfer element; evaporating water that includes a second material to deposit the second material on top of the sacrificial layer; and removing both the sacrificial layer formed on the at least one heat transfer element and the second layer formed on top of the sacrificial layer; wherein the first material is more easily removed from the at least one heat transfer element than the second material; wherein forming the sacrificial layer on a surface of the evaporator at least one heat transfer element comprises supplying water to an evaporator in operation, wherein the supplied water includes the first material; wherein the first material is provided in supersaturation for precipitation on the at least one heat transfer element until the sacrificial layer is formed in a desired thickness; further comprising raising a pH level of the supplied water comprising the first material to facilitate precipitation of said first material. 
     
     
       2. The method according to  claim 1 , wherein the pH is raised to 9 or above and/or to provide a Langelier Saturation Index greater than 0. 
     
     
       3. The method according to  claim 1 , further comprising adding the first material to the supplied water to increase a concentration of the first material in the supplied water and facilitate precipitation of the first material. 
     
     
       4. The method according to  claim 1  further comprising controlling a temperature difference between an inner side of the at least one heat transfer element in the evaporator and an outer side of the at least one heat transfer element to facilitate precipitation of the first material. 
     
     
       5. The method according to  claim 4 , wherein operating conditions for the method include controlling a temperature of the at least one of heat transfer element, a vapor that is being created during the operation of the evaporator, and the supplied water comprising the first material. 
     
     
       6. The method according to  claim 4 , wherein operating conditions for the method include controlling a period of time during which operations in the evaporator take place. 
     
     
       7. The method according to  claim 1 , wherein the first material comprises at least one of: a carbonate, bicarbonate of calcium or magnesium. 
     
     
       8. The method according to  claim 1 , further comprising, upon reaching the desired thickness, supplying further water including the first material to the evaporator, wherein the supplied further water is at least one of a) not in supersaturation with the first material and b) treated to reduce or avoid precipitation. 
     
     
       9. The method according to  claim 1 , wherein removal of the sacrificial layer and the second layer comprises supplying a chemical cleaner, wherein the chemical cleaner penetrates through the second layer to reach the sacrificial layer and remove the sacrificial layer from the at least one heat transfer element, thus removing all layers from the at least one heat transfer element into the water. 
     
     
       10. The method according to  claim 9 , further comprising removing from the water the layers removed from the at least one heat transfer element using in-line filters installed on a circulation line. 
     
     
       11. The method according to  claim 1 , wherein the removal of the sacrificial layer and the second layer comprises:
 stopping operation of the evaporator; and 
 cooling the at least one heat transfer element whereby the element shrinks causing the first material forming the sacrificial layer to break and fall from the at least one heat transfer element together with the second layer of material. 
 
     
     
       12. The method according to  claim 11 , further comprising removing the sacrificial layer of material and the second layer of material that have broken and fallen from the evaporator from a chamber where the evaporator is located. 
     
     
       13. The method according to  claim 12 , further comprising restarting operation of the evaporator after the sacrificial layer of material and the second layer of material have been removed from the chamber where the evaporator is located. 
     
     
       14. The method according to  claim 1 , wherein the second material comprises at least one of sulfate and silica.